The invention relates to a hazardous material detection system and, more particularly, to a hazardous material detection system well suited for use in detection of nitro compounds etc. that have a nitro group having a low saturated vapor pressure.
At an airport and other public facilities, it is attempted to install a hazardous material detection system that detects a nitro compound having a nitro group as a hazardous material, to prevent it from being brought into the airplane or a building. In this kind of hazardous material detection system, an atmospheric pressure ionization mass spectrometer is employed which is provided with an ion source operable at the atmospheric pressure, to analyze mass of a gaseous sample (gas to be inspected) containing a substance stuck to an incomer to be detected.
The atmospheric pressure ionization mass spectrometer introduces the gaseous sample to a corona discharge section fitted with a corona discharge needle electrode and an extraction electrode, applies a high voltage between the needle electrode and the extraction electrode to give rise to corona discharge in order to ionize the gaseous sample, introduces the ionized gaseous sample to an analysis section to analyze its mass, and outputs an analysis result to a data processor. The data processor is arranged to decide whether the gaseous sample contains the hazardous material based on the analysis result from the atmospheric pressure ionization mass spectrometer and output a result of the decision.
When it is analyzed by the atmospheric pressure ionization mass spectrometer, the gaseous sample introduced to the corona discharge section may contain non-polar to highly polar substances contained in the atmosphere as well as a dust (SiO2) and an organic substance. Furthermore, introduced the gaseous sample contains a variety of miscellaneous substances including those having a low evaporation temperature through a high evaporation temperature. When the variety of substances contained in the gaseous sample is introduced to the corona discharge section, an inside of the ion source is contaminated and foreign matter such as silicon (Si) and carbon (C) sticks to the needle electrode and the extraction electrode. When the foreign matter sticks to the needle electrode and the extraction electrode, corona discharge-becomes unstable, to deteriorate an ionization efficiency of a sample component as well. Especially if much foreign matter sticks to them, the gaseous sample cannot pass through pores in the corona discharge section, thereby disabling analysis. Therefore, it becomes necessary to clean the needle electrode and the extraction electrode, thereby requiring additional time and labor.
To prevent contamination and clogging in the ion source, such a method has been proposed that, as described in Jpn. Pat. Appln. KOKAI Publication No. Hei 6-310090 and Jpn. Pat. Appln. KOKAI Publication No. Hei 10-125276, a liquid chromatograph mass spectrometer is provided with a pore electrode cleaner, to spray a washing solvent such as methanol, acetone, or water every constant time, thereby washing the pore electrode.
The method employed in the conventional technology of using such a washing solvent as acetone, methanol, or water to wash the needle electrode and the extraction electrode cannot sufficiently remove Si and C stuck to these needle electrode and extraction electrode. Moreover, the conventional technology can be applied to the liquid chromatograph mass spectrometer but not to an atmospheric pressure ionization mass spectrometer, which analyzes mass of the gaseous sample. Further, when such washing solvent as methanol, acetone, or water is used to wash the electrodes, the inside of the ion source section, which is heated to 200xc2x0 C., is cooled down in a moment of time, thereby generating a cold spot. This causes in some cases sticking of dusts and organic substances in the gaseous sample, thereby clogging the pores.
That is, the conventional technology takes into account only washing the needle electrode and the extraction electrode if the inside of the ion source section is contaminated in connection with corona discharge but not suppressing occurrence of contamination due to ionization.
It is an object of the invention to provide a hazardous material detection system that can suppress occurrence of contamination due to ionization.
To solve these problems, the invention provides a hazardous material detection system comprising: gaseous sample introduction means for introducing a gaseous sample containing a substance stuck to a detection object; ionization means for ionizing the gaseous sample introduced by the gaseous sample introduction means, in response to an instruction; mass analysis means for analyzing mass of the gaseous sample ionized by the ionization means; and decision means for deciding whether the gaseous sample contains a hazardous material, based on an analysis result from the mass analysis means, wherein the ionization means ionizes the gaseous sample only for a time specified by the instruction.
In arrangement of the hazardous material detection system, as the gaseous sample introduction means, such means can be used as to introduce in response to an instruction a gaseous sample containing a substance stuck to a detection object, while as the ionization means, such means can be used as to ionize the introduced gaseous sample only if the gaseous sample has been introduced by the gaseous sample introduction means and, otherwise, stop ionization of the introduced gaseous sample.
Further, as the gaseous sample introduction means, such means can be used as to introduce a gaseous sample containing a substance stuck to a detection object from an inside of a detection object conveyance path which serves to manage entrance and exit of the detection object and also it can be provided with detection object detection means which outputs a detection signal when the detection object is in a detection region of the detection object conveyance path, while as the ionization means, such means can be used as to ionize a gaseous sample introduced by the gaseous sample introduction means in response to the detection signal. In this case, the ionization means can be arranged to ionize the gaseous sample only for a set time in response to the detection signal.
In arrangement of the hazardous material detection systems, various components can be added as follow.
(1) The gaseous sample introduction means is provided with a main path for introducing the gaseous sample from the detection object to the ionization means and a bypass path which discharges the gaseous sample from the detection object as bypassing the ionization means, wherein a flow rate of the gaseous sample passing through the bypass path is set larger than a flow rate of the gaseous sample passing through the main path.
(2) A filter unit for collecting dusts and organic substances contained in a fluid flowing through the main path is mounted to the main path on an upstream side of the ionization means.
Further, in arrangement of the hazardous material detection systems, alarm generation means can be provided which detects a voltage and a current of at least one of the pair of electrodes of the ionization means and, if at least one of the detected values exceeds a set value, generates an alarm to notify that a quantity of contamination generated due to ionization has exceeded a set value.
By the means, a gaseous sample is ionized only when necessary, so that occurrence of contamination due to ionization can be suppressed more effectively than in the case of ionizing the gaseous sample all the time, thereby prolonging a service life of a system.
Further, since the gaseous sample can be ionized for a prolonged time, it is possible to improve an accuracy, reproducibility, and a reliability of data obtained by mass analysis. When an alarm is generated also, it is possible to prompt cleaning of the electrodes of the ionization means.
Other objects, features and advantages of the invention will become apparent from the following description of the embodiments of the invention taken in conjunction with the accompanying drawings.